Screw

This invention relates to a screw and relates particularly to a screw with different thread flanks which are provided with different flank sections respectively.

Referring to, the US patent application publication no. 2023/0048078 discloses a conventional screwcomprising a head, a shankextending outwards from the head, and a threaded portionspirally disposed on the shank. The threaded portionhas a plurality of thread convolutionsA spirally formed on the shankand spaced apart from each other. Each thread convolutionA has two opposite first flank sectionsextending from the shank, two opposite second flank sectionsextending from the first flank sectionsrespectively, two opposite third flank sectionsextending from the second flank sectionsrespectively, a thread crestformed along a junction of the third flank sections, and a plurality of notchesrecessed into the thread crestof at least one thread convolutionA. A first thread angle θis defined between the first flank sectionsand ranges from 70 degrees to 75 degrees. A second thread angle θis defined between the second flank sectionsand ranges from 37 degrees to 43 degrees. A third thread angle θis defined between the third flank sectionsand ranges from 20 degrees to 23 degrees.

Referring to, during a screwing operation, the headreceives a rotational force in order that the thread convolutionsA are allowed to cut into a workpiece. The first, second, and third angles θ, θ, θdefined by the first, second, and third flank sections,,respectively allow the thread convolutionsA to cut the workpiecesharply, thereby reducing the screwing resistance, allowing the screwto screw into the workpiecequickly, and attaining a positioning effect.

However, the first flank sectionsare extended in a symmetric manner and have respective first sloped surfaces in cross-section. The second and the third flank sections,are also extended in a symmetric manner and have respective second and third sloped surfaces in cross-section. Although the different first, second, and third angles θ, θ, θattain effects of improving the cutting sharpness and the screwing resistance, the inventors found that the current screwis not ideal enough and made a further improvement, thereby proposing the improved screw.

The object of this invention is to provide a screw capable of increasing cutting capability while reducing screwing resistance, enhancing the strength of threaded portion, and improving a screwing effect.

The screw of this invention comprises a head, a shank extending outwards from the head, and a threaded portion spirally formed on the shank. The threaded portion has a plurality of thread convolutions spirally disposed on the shank. Each thread convolution has an upper thread flank and a lower thread flank extending outwards from the shank and opposite to each other, and a thread crest formed along a junction of the upper thread flank and the lower thread flank. A plurality of notches is recessed into the thread crest of at least one thread convolution. Each notch has a chip-guiding surface cut into the thread crest and two cutting edges formed along an outer periphery of the chip-guiding surface. Each upper thread flank has a first upper flank section extending outwards from the shank, a second upper flank section connected to the first upper flank section, and a third upper flank section connected to the second upper flank section and extended to the thread crest. Each lower thread flank has a first lower flank section extending outwards from the shank, a second lower flank section connected to the first lower flank section, and a third lower flank section connected to the second lower flank section and extended to the thread crest. Each first lower flank section and each third lower flank section are curved in shape respectively whereby the first lower flank section and the third lower flank section have respective curved surfaces in cross-section. Each second lower flank section extends between relative first and third lower flank sections without curving whereby the second lower flank section extends straightly to be in a non-curved form in cross-section. The upper and lower thread flanks with respective flank sections that are formed in an asymmetric manner can increase the strength of the threaded portion, advance the cutting capability, and decrease the screwing resistance. The first lower flank section, the third lower flank section, and the notches assist in excluding cut chips quickly and accumulating cut chips duly, thereby attaining a tight engagement. The second lower flank section is capable of providing enough supporting force. The third lower flank section also allows the threaded portion to cut into a workpiece sharply and smoothly, thereby improving the cutting effect and thread strength, attaining a quick screwing operation, and achieving a preferable screwing effect.

Preferably, the second lower flank section has a connecting segment connected to the first lower flank section and a linking segment extending between the connecting segment and the third lower flank section. The connecting segment and the linking segment have respective second lower sloped surfaces which are different from each other.

Preferably, the first upper flank section has an engaging segment connected to the shank and a stretching segment extending between the engaging segment and the second upper flank section. The engaging segment and the stretching segment have respective first upper sloped surfaces which are different from each other.

Preferably, the second upper flank section is extended straightly to provide a second upper sloped surface.

Preferably, the third upper flank section has a cutting segment connected to the second upper flank section and a severing segment extending between the cutting segment and the thread crest. The cutting segment and the severing segment have respective third upper sloped surfaces which are different from each other.

Preferably, the thread convolutions have a first plurality of thread convolutions and a second plurality of thread convolutions. The notches are recessedly formed on the first plurality of thread convolutions. The number of the first plurality of thread convolutions is in the range of one-third (⅓) to one-half (½) of the number of the thread convolutions.

Preferably, the shank defines a plurality of surface sections. Each surface section is situated between any two adjacent thread convolutions when the thread convolutions are axially spaced apart. At least one surface section is recessedly formed to define an annular groove.

Referring to, a first preferred embodiment of a screwof this invention is disclosed. The screwincludes a head, a shankextending outwards from the head, a drill portionformed on the shankand opposite to the head, and a threaded portionspirally disposed on the shank. The threaded portionhas a plurality of thread convolutionsA spirally formed on the shank. Each thread convolutionA has an upper thread flankextending outwards from the shankand facing toward the head, a lower thread flankextending outwards from the shankand facing toward the drill portion, and a thread crestformed along a junction of the upper thread flankand the lower thread flank. In this preferred embodiment, the thread convolutionsA have a first plurality of thread convolutionsAand a second plurality of thread convolutionsA. A plurality of notchesis cut into the thread crestof at least one of the first plurality of thread convolutionsA. The second plurality of thread convolutionsAis formed without any notches.

Referring to, each upper thread flankhas a first upper flank sectionconnected to the shank, a second upper flank sectionconnected to the first upper flank section, and a third upper flank sectionconnected to the second upper flank sectionand extended to the thread crest. The second upper flank sectionextends straightly between the first upper flank sectionand the third upper flank sectionto provide a second upper sloped surface in cross section. Each first upper flank sectionhas an engaging segmentA connected to the shankand a stretching segmentB extending between the engaging segmentA and the second upper flank section. Each engaging segmentA and each stretching segmentB extend without curving so that the engaging and the stretching segmentsA,B have respective first upper sloped surfaces which are different from each other in cross-section. Each third upper flank sectionhas a cutting segmentA connected to the second upper flank sectionand a severing segmentB extending between the cutting segmentA and the thread crest. Each cutting segmentA and each severing segmentB extend without curving so that the cutting and the severing segmentsA,B have respective third upper sloped surfaces which are different from each other in cross-section.

Referring to, each lower thread flankhas a first lower flank sectionconnected to the shank, a second lower flank sectionconnected to the first lower flank section, and a third lower flank sectionconnected to the second lower flank sectionand extended to the thread crest. Each first lower flank sectionand each third lower flank sectionare curved in shape respectively so that the first lower flank sectionand the third lower flank sectionhave respective curved surfaces in cross-section. Each second lower flank sectionextends between the first lower flank sectionand the third lower flank sectionwithout curving so that the second lower flank sectionextends straightly to be in a non-curved form in cross section. Each second lower flank sectionhas a connecting segmentA connected to the first lower flank sectionand a linking segmentB extending between the connecting segmentA and the third lower flank section. Each connecting segmentA and each linking segmentB extend without curving so that the connecting and the linking segmentsA,B have respective second lower sloped surfaces which are different from each other in cross-section.

Referring to, each notchhas a chip-guiding surfacerecessed into the thread crestand two cutting edgesformed along an outer periphery of the chip-guiding surface. In this preferred embodiment, the number of the first plurality of thread convolutionsAon which the notchesare disposed is in the range of one-third (⅓) to one-half (½) of the number of the plurality of thread convolutionsA.

Referring to, during a screwing operation of the screw, the drill portionis positioned against a surface of a workpiece. A rotational force is then applied to the headin order to carry out a cutting operation of the screw. The cutting segmentA and the severing segmentB of the third upper flank sectionof each upper thread flankassist the thread crestsin improving the cutting sharpness, thereby allowing the thread convolutionsA to cut into the workpiecesharply and achieving a multi-stage cutting effect. Meanwhile, the third lower flank sectionof each lower thread flankhelps reduce a contact area between the thread convolutionsA and the workpiece, thereby increasing the cutting capability and allowing the thread convolutionsA to cut into the workpiecequickly. Because the third lower flank sectionof each lower thread flankis extended in a curved manner, thereby allowing cut chips generated during the screwing operation to be discharged outwards speedily. The cut chips also can be discharged outwards through the first lower flank sectionof each lower thread flankthat is also extended in a curved manner, thereby allowing the screwto enter into the workpiecesmoothly, reducing the screwing resistance generated during the screwing operation, and enhancing the cutting capability of the thread convolutionsA.

The two-stage arrangement of each first upper flank section, namely the engaging segmentA and the stretching segmentB, and the two-stage arrangement of each second lower flank section, namely the connecting segmentA and the linking segmentB are capable of increasing the thickness of each thread convolutionA, thereby increasing the strength of the thread convolutionsA, providing better supporting force, and preventing the thread convolutionsA from being deformed or damaged during g the screwing operation while bearing larger screwing force. The upper thread flankand the lower thread flankof each thread convolutionA are formed in an asymmetric manner. The upper thread flankand the lower thread flankare provided with different number and different shape of flank sections respectively, thereby attaining a multi-stage cutting and reaming effect, severing fibers of the workpieceeffectively, accelerating the screwing operation, and reducing the screwing resistance greatly.

During the screwing operation, the cutting edgesof the notchesalso assist the thread convolutionsA in cutting the workpiece, thereby severing the fibers of the workpieceinto the cut chips and preventing the shankfrom being entangled by the fibers. Further, the cut chips are allowed to travel outwards through the chip-guiding surfacesof the notchesquickly, thereby preventing the improper accumulation of the cut chips and preventing an increase of the screwing resistance. After the screwing operation is completed, the curved first lower flank section, the curved third lower flank section, and the notchesallow a proper accumulation of the cut chips, thereby achieving a tight engagement between the screwand the workpieceand improving a screwing effect.

Referring toshow a second preferred embodiment of the screwof this invention. The correlated elements and the concatenation of elements, the operation and objectives of the second preferred embodiment are the same as those of the first preferred embodiment. This embodiment is characterized in that the thread convolutionsA are axially spaced apart so that the shankdefines a plurality of surface sectionsA each situated between any two adjacent thread convolutionsA. At least one surface sectionA is recessedly formed to define an annular groove. Thus, the annular grooveassists in reducing a contact area between the shankand the workpiece(not shown), thereby attaining a quick removal of the cut chips and a proper accumulation of the cut chips, achieving a tight engagement between the screwand the workpiece, and preventing the screwfrom being loose for attaining an anti-loosening effect.

To sum up, the screw of this invention takes advantages that the upper thread flank and the lower thread flank of each thread convolution are formed in an asymmetric manner, namely the first, second, and third upper flank sections of each upper thread flank are different the first, second, and third lower flank sections of each lower thread flank to thereby attain a multi-stage cutting and reaming effect. The second lower flank section extends straightly to be in a non-curved form between the first and third lower flank sections that are curved in shape, thereby increasing the strength of the threaded portion, providing enough supporting force, severing the fibers of the workpiece effectively, attaining a quick removal and a proper accumulation of the cut chips, reducing the screwing resistance, achieving a tight engagement, accelerating the screwing operation, and improving the screwing effect.

While the embodiments of this invention are shown and described, it is understood that further variations and modifications may be made without departing from the scope of this invention.